WDX

Electron Probe Microanalysis, EPMA, as performed in an electron microprobe combines EDS and WDX to give quantitative compositional analysis in the reflection mode from solid surfaces together with the morphological imaging of SEM. The spatial resolution is restricted by the interaction volume below the surface, varying from about 0.2 pm to 5 pm. Flat samples are needed for the best quantitative accuracy. Compositional mapping over a 100 x 100 micron area can be done in 15 minutes for major components Z> 11), several hours for minor components, and about 10 hours for trace elements. 

Before the development of semiconductor detectors opened the field of energy-dispersive X-ray spectroscopy in the late nineteen-sixties crystal-spectrometer arrangements were widely used to measure the intensity of emitted X-rays as a function of their wavelength. Such wavelength-dispersive X-ray spectrometers (WDXS) use the reflections of X-rays from a known crystal, which can be described by Bragg s law (see also Sect. 4.3.1.3)... 

Fig. 4.21. Schematic diagram of spectrometer arrangements for wavelength-dispersive and energy-dispersive X-ray spectroscopy (WDXS/EDXS) in electron microscopy.

Because of the limited energy resolution in EDX spectra an overlap of peaks can often occur, depending on the composition of the material to be analyzed. The situation is much improved in WDXS, for which the energy resolution is approximately 10 eV and better. This is demonstrated in Fig. 4.25, in which the WDX and EDX spectra recorded from BaTi03 are compared. Here, WDXS enables easy resolution of the Ba-La and Ti-Ka lines this is impossible by EDXS. In addition, for WDXS the... 

Fig. 4.25. A WDX spectrum of BaTi03 plotted against energy and compared with the corresponding EDX spectrum [4.91].

Elemental analysis can also be performed on SEM samples using x-ray spectrometer attachments [55], The techniques are known as energy dispersive x-ray (EDX) analysis and wavelength dispersive x-ray (WDX) analysis and require installation of a detector in the sample chamber. 

There are numerous types of instrumentation available for the measurement of XRF, but most of these are based either on wavelength dispersive methodology (typically referred to as WDX) or on the energy dispersive technique (typically known as EDX). For a detailed comparison of the two approaches for XRF measurement, the reader is referred to an excellent discussion by Jenkins [69]. 

The detector can be either a gas-filled tube detector or a scintillation detector, which is systematically swept over the sample, and which measures the x-ray intensity as a function of the 26 scattering angle. Through suitable calibration, each 26 angle is converted into a wavelength value for display. The major drawback associated with WDX... 

Fig. 7.17. Basic components of the apparatus used for the measurement of X-ray fluorescence by the wavelength and energy dispersive methods.WDX X-rays from the source (A) are allowed to impinge on the sample (B) the resulting XRF is discriminated by the crystal (C), and finally measured by the detector (D). EDX X-rays from the source (A) are allowed to impinge on the sample (B), and the resulting XRF is measured by the detector (D).

TGA/DTA combined thermogravimetry / differential thermal analysis WDX wavelength-dispersive X-ray diffraction... 

Within this technique, we include EDX (energy dispersive x-ray analysis), WDX (wavelength dispersive x-ray analysis), and XRF (x-ray fluorescence analysis). In all of these, x-rays emitted from a sample are analyzed. In one case, they are created by bombarding the sample with x-rays (XRF), and in the others, they are created by high energy electron beam as in an SEM (EDX, WDX). 

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